A delay line device shown in FIG. 5, one of the most basic existing arrangements using dispersion type surface acoustic wave transducers (chirp transducers) formed on a surface acoustic wave substrate 1 is practically used in a high-speed analog Fourier transformer for use in a real time spectrum analyzer or in a pulse expanding/compressing apparatus for use in a chirp radar. It usually has a wide-band property and a large delay time for purposes of improving the processing capacity and the resolving power. The substrate 1 is in the form of a monocrystal piezoelectric substrate such as lithium niobate, lithium tantalate, etc. or a multi-layer piezoelectric substrate such as AlN/sapphire, ZnO/Si, ZnO/SiO.sub.2 /Si. The arrow mark in FIG. 5 indicates the propagating direction of a surface acoustic wave.
Since the chirp transducers of the above-indicated delay line device have a large number of electrodes and a surface acoustic wave passes under a large number of electrode fingers before exiting from the transducer end, a large loss caused by internal reflections in the transducers themselves or mode transformation into a bulk wave deteriorate the characteristic of the device.
Particularly when the bands of the chirp transducers include sets of frequencies F.sub.1 and F.sub.2 in the relationship of f.sub.2 =2f.sub.1, deterioration of the characteristic by their effects cannot be disregarded. Further, a change in the sonic speed by the large number of electrodes on the propagation path causes a turbulence in the group delay and the phase characteristic.
FIG. 6 shows chirp transducers having a generally called slanted electrode arrangement in which the propagation path of an excited surface acoustic wave is gradually moved in a direction across the propagation direction, depending on the frequency of the surface acoustic wave, so as to substantially decrease the number of electrode fingers, for purposes of reducing influence of internal reflections inside the transducer and mode transform.
The above type transducers suppress the influence of internal reflections inside the transducer and mode transformation into a bulk wave and realize a good characteristic of the device. However, since the minimum size of the interdigitating width of the electrode fingers is limited and the entire electrode width in the vertical direction with respect to the surface wave propagating direction is therefore increased in order to prevent an increase in the loss caused by diffraction of a surface acoustic wave radiated from a narrow opening, the manufacturing cost per surface acoustic wave element is increased. Further, when it is used in a dispersive substrate, the design for correcting the group delay and the phase characteristic over a wide band in a single transducer is a difficult technology even with the slanted electrode arrangement.